DOCS-15247: Go Quick Start should mention installing godotenv (#95)

Author: stennie

source/quick-start.txt

@@ -39,6 +39,18 @@ Use ``go get`` to add the Go driver as a dependency.
 
    go get go.mongodb.org/mongo-driver/mongo
 
+Add Other Dependencies
+~~~~~~~~~~~~~~~~~~~~~~
+
+Use ``go get`` to add any additional dependencies. This Quick Start
+uses the ``godotenv`` package to read a MongoDB connection string
+from an environment variable to avoid embedding credentials within
+source code.
+
+.. code-block:: shell
+
+   go get github.com/joho/godotenv
+
 Create a MongoDB Cluster
 ------------------------